Internal-combustion engine with an electronically controlled hydraulic system for variable actuation of the intake valves, provided with a device for refilling the system with fluid

Abstract

In an engine having an electronically controlled hydraulic system for variable actuation of intake valves, an operating step of refilling, prior to ignition of the engine, is activated to refill a pressure chamber of the system with fluid when, after prolonged engine inactivity, the chamber has been emptied. In this refilling step, fuel supply to the engine is inhibited, and a camshaft is rotationally driven following upon activation of an engine-starting electrical machine. In this way, a pumping member associated to a tappet for actuating an intake valve is used as a pump for drawing fluid into the pressure chamber from an auxiliary fluid tank. During this step, a control valve is opened and closed in synchronism with movement of the pumping member so as to be open when the pumping member advances towards the pressure chamber and closed when the pumping member moves away from the pressure chamber.

Claims

1. An internal-combustion engine, comprising: an engine shaft and at least one cylinder that defines a combustion chamber; at least one intake duct and at least one exhaust duct, which give out into said combustion chamber; at least one intake valve and at least one exhaust valve, which are associated to said intake and exhaust ducts and are provided with respective return springs that push the valves towards a closed position; a camshaft for actuating said at least one intake valve by a respective tappet, said camshaft being driven in rotation by the engine shaft, wherein said at least one intake valve is controlled by the respective tappet, against action of the return spring, by interposition of an hydraulic arrangement that includes a pressure chamber facing which is a pumping plunger, connected to the tappet, said pressure chamber being adapted to communicate with a chamber of a hydraulic actuator associated to said at least one intake valve; an electrically actuated control valve associated to said at least one intake valve of each cylinder and adapted to set in communication said pressure chamber with a discharge volume in order to decouple said at least one intake valve from the respective tappet and cause fast closing of said at least one intake valve as a result of the respective return spring; an electronic control arrangement, for controlling said electrically actuated valve in order to vary an instant of opening and/or an instant of closing and lift of said at least one intake valve as a function of one or more operating parameters of the engine; and electrically actuated fuel-injectors, controlled by said electronic control arrangement for supplying fuel into said combustion chamber, there being associated to said engine an electrical machine for starting the engine to activate rotation of the engine shaft in a step of engine cranking, said engine being characterized in that: said pressure chamber is in communication with an auxiliary fluid tank via a non-return valve that enables passage of fluid only from said auxiliary tank in a direction of the pressure chamber, said auxiliary tank not having any direct communication with said discharge volume; and said electronic control arrangement is programmed for activating an operating cranking step of the engine prior to ignition of the engine for the purpose of refilling the pressure chamber before the engine is started, wherein the following operations are carried out: a) a supply of fuel to said combustion chamber is inhibited; b) said electrical machine is activated for setting in rotation the engine shaft and consequently said camshaft so that a reciprocating motion of said pumping plunger is activated; c) said electrically actuated control valve is cyclically opened and closed, in synchronism with movement of said pumping plunger, in such a way that said control valve is open in a step where the pumping plunger advances towards the pressure chamber and is closed in a step where the pumping plunger moves away from said pressure chamber so that the pumping plunger functions as a suction pump for recalling fluid from said auxiliary tank to the pressure chamber; and d) after a time interval, the supply of fuel to said combustion chamber is enabled and the electrically actuated control valve is kept closed to obtain actuation of the intake valves and ignition of the engine.

2. The engine according to claim 1, wherein said time interval is a pre-set time interval.

3. The engine according to claim 1, wherein said time interval corresponds to a pre-set number of cycles of forward and backward movements of the pumping plunger.

4. The engine according to claim 1, further comprising a pressure sensor adapted to detect pressure in the pressure chamber and to issue a signal that is received by said electronic control arrangement and in that said time interval corresponds to an amount of time necessary for said pressure sensor to warn that a pre-set value of the pressure in the pressure chamber has been exceeded.

5. The engine according to claim 1, wherein a sensor arrangement is provided, adapted to detect movement of said at least one intake valve and in that said electronic control arrangement is programmed for activating the operating step prior to ignition of the engine for refilling the pressure chamber when, in the step of engine cranking, absence of movement of said at least one intake valve is detected.

6. The engine according to claim 5, wherein said sensor arrangement comprises a pressure sensor for detecting pressure in an intake manifold of the engine, and is adapted to issue a signal that is received by said electronic control arrangement.

7. The engine according to claim 5, wherein said sensor arrangement comprises an accelerometer associated to said at least one intake valve, the signal of which is received by said electronic control arrangement.

8. The engine according to claim 1, wherein a pressure sensor is provided, adapted to detect pressure in the pressure chamber and to issue a signal that is received by said electronic control arrangement, and in that said electronic control arrangement is programmed for activating the operating step prior to ignition of the engine for refilling the pressure chamber when, in the step of engine cranking, a pressure in the pressure chamber lower than a pre-set threshold value is detected.

9. The engine according to claim 1, wherein said auxiliary fluid tank is connected to said pressure chamber by a connection duct having a first end that communicates with the pressure chamber on a downstream side of the control valve, opposite to a side of said discharge volume, and a second end connected to said auxiliary tank in a bottom part of said tank, and in that, in a normal condition of use of the engine, said second end is situated at a level lower than a level of said first end, and also than a level of the actuators of the intake valves and than a level of the pumping plunger, said actuators and said pumping plunger being consequently at a height greater than zero with respect to an outlet of the auxiliary tank.

10. The engine according to claim 9, wherein said auxiliary tank is also connected to a channel for supplying pressurized fluid, which communicates with said auxiliary tank in a top part of said auxiliary tank.

11. The engine according to claim 10, wherein said auxiliary tank has at least one top opening for venting into atmosphere.

12. A method for control of an internal-combustion engine, the engine comprises: an engine shaft and at least one cylinder that defines a combustion chamber; at least one intake duct and at least one exhaust duct, which give out into said combustion chamber; at least one intake valve and at least one exhaust valve associated to said intake and exhaust ducts and provided with respective return springs that push the valves towards a closed position; a camshaft for actuating said at least one intake valve by a respective tappet, said camshaft being driven in rotation by the engine shaft, wherein said at least one intake valve is controlled by the respective tappet, against action of the return spring, by interposition of an hydraulic arrangement that includes a pressure chamber facing which is a pumping plunger, connected to the tappet, said pressure chamber being adapted to communicate with a chamber of a hydraulic actuator associated to said at least one intake valve; an electrically actuated control valve associated to said at least one intake valve of each cylinder and adapted to set in communication said pressure chamber with a discharge volume in order to decouple said at least one intake valve from the respective tappet and cause fast closing of said at least one intake valve as a result of the respective return spring; an electronic control arrangement, for controlling said electrically actuated valve in order to vary an instant of opening and/or an instant of closing and lift of said at least one intake valve as a function of one or more operating parameters of the engine; and electrically actuated fuel-injectors, controlled by said electronic control arrangement for supplying fuel into said combustion chamber, there being associated to said engine an electrical machine for engine cranking to activate rotation of the engine shaft in a step of engine cranking, said method being characterized in that: said pressure chamber is in communication with an auxiliary fluid tank via a non-return valve that enables passage of fluid only from said auxiliary tank in a direction of the pressure chamber, said auxiliary tank not having any direct communication with said discharge volume; and in that an operating cranking step of the engine is activated prior to ignition of the engine for the purpose of refilling the pressure chamber before the engine is started, wherein the following operations are carried out: a) supply of fuel to said combustion chamber is inhibited; b) said electrical machine is activated for setting in rotation the engine shaft and consequently said camshaft so that a reciprocating motion of said pumping plunger is activated; c) said electrically actuated control valve is cyclically opened and closed, in synchronism with movement of said pumping plunger in such a way that said control valve is open in a step where the pumping plunger advances towards the pressure chamber and is closed in a step where the pumping plunger moves away from said pressure chamber so that the pumping plunger functions as a suction pump for recalling fluid from said auxiliary tank into the pressure chamber; and d) after a time interval, the supply of fuel to said combustion chamber is enabled and the electrically actuated control valve is kept closed to obtain actuation of the intake valves and ignition of the engine.

13. The method according to claim 12, wherein said time interval is a pre-set time interval.

14. The method according to claim 12, wherein said time interval corresponds to a pre-set number of cycles of forward and backward movements of the pumping plunger.

15. The method according to claim 12, wherein the engine comprises a pressure sensor adapted to detect pressure in the pressure chamber and to issue a signal that is received by said electronic control arrangement and in that said time interval corresponds to an amount of time necessary for said pressure sensor to warn that a pre-set value of the pressure in the pressure chamber has been exceeded.

16. The method according to claim 12, wherein a sensor arrangement is provided, and is adapted to detect movement of said at least one intake valve and in that the operating step prior to ignition of the engine for refilling the pressure chamber is activated when, in the step of engine cranking, absence of movement of said at least one intake valve is detected.

17. The method according to claim 16, wherein said sensor arrangement comprises a pressure sensor for detecting pressure in an intake manifold of the engine, and is adapted to issue a signal that is received by said electronic control arrangement.

18. The method according to claim 16, wherein said sensor arrangement comprises an accelerometer associated to said at least one intake valve, the signal of which is received by said electronic control arrangement.

19. The method according to claim 12, wherein a pressure sensor is provided, adapted to detect pressure in the pressure chamber and to issue a signal that is received by said electronic control arrangement, and in that the operating step prior to ignition of the engine for refilling the pressure chamber is activated when, in the step of engine cranking, a pressure in the pressure chamber lower than a pre-set threshold value is detected.

Description

DESCRIPTION OF A PREFERRED EMBODIMENT

(1) Further characteristics and advantages of the invention will emerge from the ensuing description with reference to the annexed drawings, which are provided purely by way of non-limiting example and in which:

(2) FIG. 1, already described above, illustrates in a cross-sectional view the cylinder head of an internal-combustion engine provided with a MULTIAIR system for variable actuation of the intake valves, according to what is illustrated in the document No. EP 0 803 642 B1;

(3) FIG. 2, which has also already been described above, illustrates the control system of two intake valves associated to one and the same cylinder of the engine, in a MULTIAIR system of the conventional type described, for example, in EP 2 261 471 A1;

(4) FIG. 3, which has also already been described above, illustrates a diagram of the hydraulic system according to the known art;

(5) FIG. 4, which has also already been described above, illustrates the diagrams of lift of the intake valves and a mode of control of the electrical valve of the system according to the known art;

(6) FIG. 5 illustrates a diagram similar to that of FIG. 3, but modified according to the teachings of the present invention;

(7) FIGS. 6A and 6B are diagrams of an internal-combustion engine applied to which is the system according to the invention; and

(8) FIG. 7 illustrates a diagram similar to that of FIG. 4 that shows an operating mode of control of the electrical valve in the system according to the invention.

(9) FIGS. 1-4 have already been described above. With reference to FIG. 5, the parts in common with those of FIG. 3 are here designated by the same reference numbers.

(10) A first characteristic of the system according to the invention lies in the fact that it comprises an auxiliary fluid tank 600 that is not in communication with the exhaust channel 23 upstream of the solenoid valve 24. The auxiliary tank 600 is filled with fluid during normal operation of the engine, in so far as it has an inlet 601 connected to a branch 803 of the delivery duct 800 of the pump 900. The inlet 601 is set in the top part of the aforesaid tank, which is closed at the top by a lid having at least one opening 602 for venting into the atmosphere.

(11) The auxiliary tank 600 has an outlet, adjacent to its bottom, connected to one end 603 of a duct 604, the opposite end 605 of which communicates with the pressure chamber C, downstream of the channel 23 and of the solenoid valve 24. In the example illustrated, the duct 604 gives out into the duct d3. Set in the connection duct 604 is a non-return valve 700 that enables passage of fluid only in the direction that goes from the tank 600 to the duct d3.

(12) In the normal condition of use of the engine, the end 603 of the connection duct 604 is at a level lower than the end 605 connected to the pressure chamber. Furthermore, this end 603 occupies a lower position than the two areas of possible leakage of oil, which are represented by the area of the pumping plunger 16 and by the lowest areas of the actuators 21. Consequently, such areas of possible leakage of oil are, respectively, at a height H1 and at a height H2, with H1>0 and H2>0, with respect to the outlet of the auxiliary tank (see FIG. 5). Consequently, even in the case of a very long period of inactivity of the engine, and even in the case where the hydraulic system downstream of the non-return valve 400 empties completely on account of leakage of fluid through the actuators 21, the tank 600 continues to be full of fluid. The purpose of this tank is in fact to ensure always and in any case an additional fluid capacity, even following upon long periods of inactivity of the engine.

(13) The electronic control unit 25 is programmed for activating an operating step of refilling of the hydraulic system prior to ignition of the engine. According to this operating mode, the electronic control unit 25 inhibits supply of fuel to the cylinders of the engine, while the step of engine cranking is activated.

(14) FIG. 6A of the annexed drawings is a schematic illustration of the usual arrangement of an internal-combustion engine with an engine shaft 50 having one end carrying a flywheel 51 bearing a ring gear that can be engaged by a pinion 52 carried by the shaft of an electrical machine 53 pre-arranged for engine cranking. The opposite end of the engine shaft 50 carries a pulley or gear 54 that drives in rotation, by means of a cogged-belt or chain transmission 55, a pulley or gear 56 mounted on an end of the camshaft 11. Consequently, during engine cranking, when the electrical machine 53 is activated, the engine shaft 50 is set in rotation and transmits a rotation (with transmission ratio 1:2) to the camshaft 11.

(15) FIG. 6B of the annexed drawings is a schematic illustration of an internal-combustion engine with four cylinders CY1, CY2, CY3, CY4 that receive air from an intake manifold IM and fuel from injectors I1, I2, I3, I4 electronically controlled by a control unit 1000 (which may coincide with the control unit 25 already described above).

(16) According to the invention, in the aforesaid refilling step prior to ignition of the engine, the electronic control unit 1000 inhibits supply of fuel to the engine so that the engine remains off. Each cam 14 of the camshaft is instead set in rotation, in so far as the camshaft is turned, as already referred to above, by the electrical starting machine 53.

(17) With reference to FIG. 5, during the aforesaid refilling step prior to ignition of the engine, the rotation of the cam 14 determined by the electrical starting machine 53 causes a reciprocating motion of the pumping plunger 16, which cannot, however, bring about a movement of the intake valves 7 in so far as the pressure chamber C is empty.

(18) Once again in said refilling operating mode prior to the step of ignition of the engine, the electronic control unit 25 is programmed for controlling the solenoid valve 24 in such a way as to open it and close it cyclically in synchronism with the movement of the pumping plunger 16 caused by the cam 14. More precisely, in this refilling operating step, the solenoid valve 24 is opened in the step where the pumping plunger advances towards the chamber C, and is closed in the step where the pumping plunger moves away from the chamber C. During its movement of advance towards the chamber C, the pumping plunger 16 expels towards the channel 23 the air contained in the volume downstream of the solenoid valve 24, whereas during each movement of recession from the chamber C, which occurs with the solenoid valve 24 closed, the pumping plunger 16 brings about a negative pressure that causes a passage of fluid from the supplementary tank 600 into the duct d3, through the connection duct 604 and the non-return valve 700.

(19) Consequently, after a given time interval, in which the electrical machine 53 continues to control rotation of the cam 14, the pumping plunger 16 manages to fill completely the volume of the system downstream of the solenoid valve 24 so that the supply of fuel can be enabled and the solenoid valve 24 returns to being controlled in the conventional way so as to enable opening of the intake valves 7 and ignition of the engine.

(20) FIG. 7 is a schematic illustration of the mode of control of the solenoid valve 24 during the operating step described above prior to ignition of the engine, where the pumping plunger 16 is used as pump for taking in fluid from the tank 600 into the volume of fluid downstream of the solenoid valve 24, until this volume is filled. As shown in FIG. 7, closing of the solenoid valve is controlled at an instant to, when the solenoid of the solenoid valve is supplied with a peak current adapted to cause movement of the mobile member of the solenoid valve. This closing occurs substantially immediately before the pumping plunger 16 again recedes after a stroke of advance, following upon rotation of the cam 14 (the profile of lift of which is once again illustrated in FIG. 7). As is also illustrated in FIG. 7, the current signal supplied to the solenoid is then lowered to a lower non-zero (hold) value, which keeps the solenoid valve closed, up to an instant t.sub.1, when the current goes back to zero and the solenoid valve consequently opens. The instant t.sub.1 is immediately prior to a new stroke of advance of the pumping plunger 16 towards the pressure chamber C.

(21) In a first embodiment, once the aforesaid operating step prior to ignition of the engine is activated, it is continued for a fixed and pre-set time interval, after which the supply of fuel is enabled and the electronic control unit 25 returns to the usual operating mode in order to cause engine ignition. This fixed and pre-set time can be established for each individual type of engine through testing. The electronic control unit can then be programmed so as to implement the aforesaid operating step prior to ignition of the engine for a fixed duration, judged in any case sufficient for guaranteeing that the volume of the system on the pressure side is totally filled with fluid and the system is again completely operative.

(22) The same result can be obtained by programming the electronic control unit for implementing the aforesaid operating step of refilling prior to ignition of the engine for a given number of cycles of movements of advance and recession of the pumping plunger 16 associated to each cylinder.

(23) Alternatively, it is also possible to provide a pressure sensor PS (FIG. 5) associated to the volume of the system downstream of the solenoid valve 24, the signal of which is received by the electronic control unit 25. In this case, the electronic control unit can be programmed for prolonging the aforesaid refilling operating step, prior to ignition of the engine, until the aforesaid pressure sensor PS warns that a pre-set value of the pressure in the volume of fluid downstream of the solenoid valve 24, for each cylinder of the engine, has been exceeded.

(24) Preferably, the aforesaid operating step of refilling prior to ignition of the engine is enabled by the electronic control unit only when the need arises. For the purpose, sensor means are provided adapted to detect directly or indirectly the movement of the intake valves in such a way that the aforesaid operating step of refilling prior to ignition of the engine is activated only when, in the step of engine cranking, absence of movement of the intake valves of one or more cylinders is detected. To obtain this result it is possible to exploit, for example, a pressure sensor IMS (FIG. 6B) adapted to detect the pressure in the intake manifold IM of the engine. This sensor is usually provided in association with the fuel-injection control system. The signal issued by the pressure sensor in the intake manifold IMS is sent to the electronic control unit (for example, the unit 1000) and enables this to detect when the intake valves of one or more cylinders remain closed so as to activate accordingly the refilling operating mode prior to engine ignition.

(25) Alternatively, it is also possible to provide an accelerometer VS (FIG. 5) associated to each intake valve 7, the signal of which is received by the electronic control unit 25 and enables immediate detection of a possible absence of movement of the intake valve.

(26) As an alternative to the aforesaid solutions, the need to activate the refilling operating mode prior to ignition of the engine may be detected by providing a pressure sensor PS in the volume of fluid downstream of the solenoid valve 24, the signal of which is received by the electronic control unit 25 in such a way that the operating step of refilling prior to ignition of the engine can be activated when in the step of engine cranking a pressure in the aforesaid volume of fluid lower than a pre-set threshold value is detected.

(27) Whatever the solution selected, the system is able, upon engine ignition by the driver, to determine whether it is necessary to proceed to an operating step of refilling before engine ignition. If this need is detected, the system activates the above operating mode, keeping the engine turned off and using the electrical starting machine 53 for setting each cam 14 in rotation and accordingly using the pumping plunger 16 associated to each cylinder of the engine for filling again the volume of the system downstream of the solenoid valve 24 with fluid. As has been mentioned, this is obtained in so far as the pumping plunger 16 acts as suction pump, which is able to draw in fluid from the supplementary tank 600 into the volume of the system downstream of the solenoid valve 24 until complete filling of this volume is obtained. After a pre-set time interval, or after a pre-set number of cycles of movements of advance and recession of the pumping plunger 16 associated to each cylinder, or else when a pressure sensor associated to the volume of fluid downstream of the solenoid valve 24 detects that a pre-set pressure threshold value for each cylinder of the engine has been reached, the system enables supply of the fuel and returns to the normal mode of control of the solenoid valve 24 in order to bring about ignition of the engine.

(28) As has likewise already been mentioned, the tank 600 is pre-arranged in a condition completely isolated from the exhaust channel 23, with the outlet 603 set at a level lower than both the end of the connection duct 604 that communicates with the volume of fluid downstream of the solenoid valve 24 and the areas of the pumping plunger 16 and of the actuators 21 where there may arise leakage of fluid (differences in level H1 and H2 in FIG. 5). Consequently, it is guaranteed that the tank 600 always ensures the presence of a fluid reserve, even after prolonged inactivity of the engine.

(29) Of course, without prejudice to the principle of the invention, the details of construction and the embodiments may vary widely with respect to what is described purely by way of example herein, without thereby departing from the scope of the claims.